Bioabsorbable coatings of surgical devices

ABSTRACT

Methods of reducing device drag on implantable articles are disclosed herein. The methods include coating the contact surfaces of implantable articles with bioabsorbable lubricating coatings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/748,866 filed on Mar. 29, 2010 entitled “Bioabsorbable Coatings ofSurgical Devices,” which is a continuation of U.S. patent applicationSer. No. 10/027,891 filed on Dec. 20, 2001 entitled “BioabsorbableCoatings of Surgical Devices,” each of which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to bioabsorbable coatings for implantablemedical devices, more specifically, to bioabsorbable implantable medicaldevices with improved lubricity.

BACKGROUND OF THE INVENTION

In medical procedures, the movement of a surface of an implantabledevice with respect to tissue is important in reducing damage to boththe surface and to the tissue. Damage to tissue as a result of “tissuedrag” friction is know to cause inflammation and pain, and may lead to alonger recovery time. High friction between a surface material of animplant and blood may result in clotting and subsequent occlusion of ablood vessel. Friction may also damage the implant material, thusrendering it ineffective or shortening its useful life.

The problem of “tissue drag” has been of concern to the medicalprofession for some time. For example, it is know to improve thelubricity of a braided polyethylene terephthalate suture by applying acoating to the outer surface of the suture consisting of polymers ofpolyethylene or polytetrafluoroethylene (PTFE) having a lowercoefficient of friction than the surface of the suture. It is also knownthat sutures coated with dimethylsiloxane-alkylene oxide copolymers haveimproved handling characteristics. These polymers, however, are notbioabsorbable, and therefore leave a residue in the tissue.

The use of certain bioabsorbable polymers as coatings to improve thetie-down performance of sutures and to also reduce tissue drag issimilarly known in this art. These coatings may include copolymers andblends containing monomers of lactide, glycolide, epsilon-caprolactone,trimethylene carbonate, p-dioxanone, ethylene oxide, and propyleneoxide.

The reduction of tissue drag using bioabsorbable polymers as coatings onimplantable medical devices other than sutures has also known. Thecoated devices include, for example, screws and suture anchors, havingsurfaces that drag along and contact both soft and hard tissue duringimplantation.

Many implantable medical devices, such as hip or knee prostheses, arestructured such that, during their life, or during the medical procedurefor implantation, there is movement of a surface of the device againstanother surface of the device. This relative movement, or articulation,of one surface against another, is known as “device drag”. In devicedrag, friction may damage the material of the surface, thus rendering itineffective or shortening its useful life.

The issues of device drag in non-bioabsorbable implantable medicaldevices have been addressed in a variety of ways. For example, it isknown to apply a thin layer of a low coefficient of friction coating(ceramic or diamond-like carbon) on one or more contact surfaces. Such acoating reduces friction between the surfaces of a bone fixing deviceformed from conventional implantable materials such as titanium alloysand solids ceramics.

Also, with regard to implantable orthopedic prostheses having a metallicfirst component having a first bearing surface, and a second metalliccomponent having a second bearing surface, where the second bearingsurface is disposed in opposition to the first bearing surface in asliding bearing relationship, it is known to provide on at least one ofthe first and second bearing surfaces a plurality of substantiallyevenly distributed plateaus interspersed with valleys. The valleys havea depth of about 0.0002 inch to about 0.002 inch below the plateaus tofacilitate lubrication of the articulating surfaces by natural bodyfluids.

Although the issue of device drag has been addressed innon-bioabsorbable implantable medical devices, there is a desire in manyapplications to move away from non-absorbable implants. A majordisadvantage of non-bioabsorbable implantable medical devices is thatthey remain permanently in the body. It is known that these implants cancause a variety of problems after healing, for example, chronicirritation and inflammation of surrounding body tissue, abrading oftissue during normal motion of the joint, and problems in X-ray imagingin follow-up examinations since the implant may block out the view ofthe tissue. When complications do arise from non-bioabsorbableimplantable medical devices additional surgical procedures may berequired to remove problematic devices once the tissue has healed,placing the patient at additional risk.

Bioabsorbable implantable medical devices are naturally degradable bythe body, through known mechanisms including bioresorption andbiodegradation. Accordingly, contact with surrounding tissue afterimplantation does not necessitate surgical intervention because thedevice will be completely absorbed by the body once the tissue hashealed. Reducing device drag is particularly advantageous in polymericbioabsorbable devices where the device is inserted in hard body tissuessuch as bone using a driver that engages the device. The driver/deviceconnection or engagement location is susceptible to failure if the loadresulting from tissue drag exceeds the strength of such connection orengagement location. By reducing tissue drag, the load necessary toinsert the device is typically decreased, reducing the risk of failureat the driver/device connection, or failure to other parts of the deviceas well.

The problems of tissue drag and device drag in implantable medicaldevices have been of concern to the medical profession for some time. Inimplantable devices that drag along tissue, both non-bioabsorbable andbioabsorbable coatings have been reported. In non-bioabsorbableimplantable medical devices, there have been attempts to reduce devicedrag using non-bioabsorbable low friction coatings or surfacemodification. However, device drag in bioabsorbable implantable medicaldevices, particularly occurring during implantation, or when there isarticulation of surfaces, has been given little attention.

Accordingly, there is a need in this art for methods of reducing devicedrag in bioabsorbable implantable medical devices while maintaining thebioabsorbable nature of the devices.

SUMMARY OF THE INVENTION

Therefore, it is an object of this invention to provide methods ofreducing device drag in bioabsorbable implantable medical devices whileretaining the bioabsorbable characteristics of the device.

It is yet another object of the present invention to provide a coatedsubstrate, wherein the substrate is a bioabsorbable material and thecoating is a bioabsorbable lubricating material.

Accordingly, a coated bioabsorbable medical device is disclosed. Thedevice has a first bioabsorbable contact surface. It also has a second asecond bioabsorbable contact surface for engagement with the firstcontact surface. A bioabsorbable coating is disposed on at least asection of the second contact surface for reducing device drag.

Another aspect of the present invention is a coated bioabsorbablemedical device. The device has a first bioabsorbable contact surface anda second bioabsorbable contact surface for engagement with the firstcontact surface. A bioabsorbable coating disposed on at least a sectionof both the first and second contact surfaces.

Yet another aspect of the present invention is a coated bioabsorbablemedical device. The device has a first member having a first contactsurface and a second member having a second contact surface. The secondmember engages the first member such that the first and second contactsurfaces are approximated. A bioabsorbable coating is disposed on atleast a portion of the second contact surface such that said coatingengages the first contact surface. Optionally, the first contact surfacealso has a bioabsorbable coating disposed on at least a portion thereof.

Still yet another aspect of the present invention is a method of usingthe above-described medical devices.

These and other objects and advantages of the present invention will beapparent from the following description invention as illustrated in thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bioabsorbable implantable bone platesystem of the present invention having a bioabsorbable lubricatingcoating on its dragging surfaces in accordance with a first exemplaryembodiment of the invention.

FIG. 2 is a cross-sectional view of the device system of FIG. 1 takenalong View Line 2-2 showing the bone screws implanted in bone.

FIG. 3 is a perspective view of a bioabsorbable implantable ligamentrepair device of the present invention having bioabsorbable lubricatingcoatings on its dragging surfaces in accordance with a second exemplaryembodiment of the invention.

FIG. 4 is a partial cross-sectional view of the device of FIG. 3 takenalong View Line 4-4; the distal end of the sheath member is shown inphantom lines.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to bioabsorbable coatings forbioabsorbable implantable medical devices to counteract device drag onthe device surfaces during implantation or operation of the devices. Thecoatings reduce device drag in the devices while maintaining thebioabsorbable nature of the devices.

Referring to FIG. 1, a coated bioabsorbable implantable bone platesystem of the present invention is illustrated. A similar bioabsorbablebone plate system without the lubricating bioabsorbable coating isdescribed in U.S. Pat. No. 6,093,201, entitled “Biocompatible AbsorbablePolymer Plating System for Tissue Fixation”, which is incorporated byreference.

The bioabsorbable plate system 10 is seen to have a plate member 20having top surface 30 and bottom surface 35. Member 20 is seen to have aplurality of radial projections 40 having proximal ends 42 and distalcurved ends 44.

The radial projections 40 are seen to have fastener-receiving openings42 extending therethrough. Plate member 20 is also seen to have acentral fastener receiving opening 25 extending therethrough. Preferablythe openings 25 are round but can have other geometric configurations.The openings 42 are seen to have sidewalls 27. The sidewalls 27 havebeveled, angulated sidewall sections 29.

A cross-sectional view of plate member 20 is illustrated in FIG. 2. Asseen in FIG. 2, the plate member 20 is seen to have coating 50 on topsurface 30 and bottom surface 35. Coating 50 is also seen to be coveringsidewalls 27 and angulated sections 29.

Referring to FIGS. 1 and 2, the plate system 10 is also seen to have aplurality of fasteners 80. The fasteners 80 are seen to be bioabsorbablebone screws having a root section 82 and a driving head 100. Rootsection 82 is seen to have exterior surface 84, pointed distal end 86,proximal end 87, and a plurality of thread flights 88 extending fromexterior surface 84. The thread flights are seen to have exteriorsurface 89. The driving head 100 is seen to extend from proximal end 87of root section 82. The driving head member 100 is seen to have a flatproximal surface 102 containing engagement cavity 104. Preferably theengagement cavity is a slot, but can have other configurations such as acavity to accept conventional drivers such as Phillips head screwdrivers, Torx screw drivers, Allen wrenches and the like and equivalentsthereof. Head 100 is seen to have distal taping section 105 having outersurface 107. As seen in FIG. 2, the fastener 80 is seen to have coating110 covering the outer surfaces.

When used in a surgical procedure, the surgeon prepares the patent in aconventional manner and then exposes the surface 125 of a bone 120 inthe patient's body to which the bone plate is to be mounted usingconventional surgical techniques. The surgeon then affixes the plate 20to the bone surface 125 by drilling pilot holes 127 through openings 25in a conventional manner by using conventional surgical drillingapparatus and techniques. The fasteners 80 are then inserted throughopenings 25 into pilot holes 127, and the surgeon screws the fasteners80 into the bone 120 using conventional devices such as a screw driver,wrench, etc. As the fasteners 80 are being employed, the coating 110 onouter surfaces 84 and 89 and surface 107 of fastener 80 engage thecoating 50 on the sidewalls 44 and 46 in openings 40. The presence ofcoatings 50 and 110 reduces device drag. Coating 110 may also reducetissue drag as well in bone 120. If desired, in the practice of thepresent invention the surface of only one of the devices may be coated,and the surface of the other left uncoated.

FIGS. 3 and 4 illustrates a second embodiment of a bioabsorbableimplantable medical device of the present invention, wherein thecomponents have coated surfaces to reduce device drag. Referring to FIG.3, a coated bioabsorbable graft ligament anchor system 200 isillustrated. A similar, but uncoated, bioabsorbable graft ligamentanchor system is described in commonly assigned, copending U.S. patentapplication Ser. No. 09/966,766, entitled “Graft Ligament Anchor andMethod for Attaching a Graft Ligament to a Bone”, filed on Sep. 28,2001, the disclosure of which is incorporated by reference.

Referring first to FIG. 3, the graft ligament anchor system 200 is seento have a selectively radially expandable sheath member 220 and a sheathexpanding member 260. Radially expandable sheath member 220 is seen tohave wall 231, proximal end 232 and distal end 234, inner surface 236,outer surface 238 and central lumen 240. The sheath member 220 hasproximal opening 242 and distal opening 244, both of which are incommunication with lumen 240. Sheath member central lumen 240 issufficiently sized to effectively receive and engage sheath-expandingmember 260. Extending up from the outer surface of wall 231 are theridged members 250 having outer surfaces 251 and inner pockets 255having inner surfaces 256, said pockets 255 being in communication withlumen 240. The sheath member 220 is seen to have coating 248 upon theinner surface 236 and the outer surface 238, as well as on surfaces 256and 251. Sheath expanding member 260 is seen to have proximal and distalends 262 and 264, respectively.

The sheath expanding member 260 has outer surface 265 and a centrallongitudinal cannulation 268 extending therethrough. Extending outwardlyfrom the outer surface 265 are a plurality of thread flights 270 havingouter surfaces 272. The sheath expanding member 260 is also seen to havecoating 280 upon outer surface 265 and outer surfaces 272.

During deployment of graft ligament anchor system 200, sheath expandingmember 260 is inserted into sheath member central lumen 240 ofexpandable sheath member 220 and engages member 210 such that it expandsradially. An insertion tool (not shown) is disposed into the centralcannulation 268 of sheath expanding member 220 to drive expanding member260 into sheath central lumen 240 by rotating the member 260. Rotationof member 260 causes threads 270 to engage pockets 255.

During insertion, outer surface 265 of sheath expanding member 260 andthread surfaces 272 drag along inner surface 236 of radially expandablesheath member 220 and inner surfaces 256 of pockets 255. This drag mayresult in friction, which could cause damage to some or all of thesesurfaces. The bioabsorbable coatings 248 and 280 of the presentinvention reduce the device drag and limit damage to these surfaces.Reduced device drag also reduces the insertion energy, and may bemeasured for example in insertion torque, of an insertion tool (notshown) as it drives expanding element 260 into sheath central lumen 240.

The bioabsorbable devices that have contact surfaces that may be coatedaccording to the present invention are not limited to the bone screws,bone plates and ligament attachment systems described herein. Anybioabsorbable medical device having contact surfaces that engage eachother, whether during insertion, after insertion, or both during andafter insertion may be coated to decrease device drag. The devicesinclude but are not limited to various types of conventionalbioabsorbable medical devices such as orthopedic screws, bone plates,prostheses, anastomosis devices, grafts, suture anchors, orthopedicimplants, spinal implants, joint replacements, vascular prostheticdevices, sort tissue implants, tissue fixation devices and the like.

The bioabsorbable medical devices of the present invention havingcontact surfaces will be made from conventional biocompatible,bioabsorbable polymers. They may be organic or inorganic, synthetic ornatural. Examples of suitable biocompatible bioabsorbable polymersinclude biopolymers such as aliphatic polyesters, poly(amino acids),copoly(ether-esters), polyalkylenes oxalates, polyamides, poly(ethyleneglycol), poly(iminocarbonates), polyorthoesters, polyoxaesters,polyamidoesters, polyoxaesters containing amine groups,poly(anhydrides), polyphosphazenes, biomolecules, and copolymers andblends thereof. For the purpose of this invention, aliphatic polyestersinclude but are not limited to homopolymers and copolymers of lactide(which includes lactic acid, D-, L- and meso lactide), glycolide(including glycolic acid), ε-caprolactone, paradioxanone(1,4-dioxan-2-one), trimethylene carbonate (1,3-dioxan-2-one), alkylderivatives of trimethylene carbonate, monoglyceride polyesters,δ-valerolactone, β-butyrolactone, γ-butyrolactone, ε-decalactone,hydroxybutyrate, hydroxyvalerate, 1,4-dioxepan-2-one (including itsdimer 1,5,8,12-tetraoxacyclotetradecane-7,14-dione), 1,5-dioxepan-2-one,6,6-dimethyl-1,4-dioxan-2-one 2,5-diketomorpholine, pivalolactone,alpha, alpha-diethylpropiolactone, ethylene carbonate, ethylene oxalate,3-methyl-1,4-dioxane-2,5-dione, 3,3-diethyl-1,4-dioxan-2,5-dione,6,8-dioxabicycloctane-7-one and polymer blends thereof. Thebiocompatible, bioabsorbable inorganics include ceramics composed ofmono-, di-, tri-, alpha-tri, beta-tri, and tetra-calcium phosphate,hydroxyapatite, fluoroapatites, calcium sulfates, calcium fluorides,calcium oxides, calcium carbonates, magnesium calcium phosphates,bioglasses, and mixtures thereof. The devices of the present inventionmay also be made of composites of conventional bioabsorbable polymersand bioabsorbable inorganics. The devices of the present invention mayadditionally be made from natural biopolymers including collagen,elastin, alginate, chitin, hyaluronic acid, mono-, di- andpolysaccharides, and gelatin.

Although it is desirable to coat the contact surfaces of both elementsthat are in contact or engagement, it is also within the purview of thepresent invention to coat only one engagement surface, or portions ofone or both engagement surfaces to provide for increased lubricity andreduced device drag.

The coatings which are applied to the surfaces of the coated devices ofthe present invention will be sufficiently thick to provide effectivelubricity and reduction of device drag. Of course the thickness willalso depend upon the type of device and its application within the body,as well as the type of coating. However, for the devices describedabove, the thickness of the coatings will typically vary from about 1.0to about 10.0 microns, more typically about 1.0 to about 5.0 microns,and preferably about 2 to about 5 microns.

When applying coatings to two contact surfaces, the same coatingcomposition may used, or a different coating compositions may be used oneach contact surface. If desired, multiple coats of the coatings may beapplied. In addition, a base coat of a first coating composition may beapplied over a contact surface, and a top coat of a second coatingcomposition may be applied over the base coat.

The coatings useful in the practice of the present invention are lowcoefficient of friction biocompatible, bioabsorbable materials. They maybe inorganic or organic compounds or blends of both. They may be lowmolecular weight compounds or biopolymers. They may be in either solidor liquid form, or a mixture of both, such as in a microdispersion, andmay be either a naturally occurring or synthetic, or blends of both.Natural biopolymers include collagen, elastin, alginate, chitin,hyaluronic acid, mono-, di- and polysaccharides, and gelatin.

Examples of suitable biocompatible, bioabsorbable biopolymers that couldbe used include biopolymers such as aliphatic polyesters, poly(aminoacids), copoly(ether-esters), polyalkylenes oxalates, polyamides,poly(ethylene glycol), poly(iminocarbonates), polyorthoesters,polyoxaesters, polyamidoesters, polyoxaesters containing amine groups,poly(anhydrides), polyphosphazenes, biomolecules, and copolymers andblends thereof.

For the purpose of this invention aliphatic polyesters include but arenot limited to homopolymers and copolymers of lactide (which includeslactic acid, D-, L- and meso lactide), glycolide (including glycolicacid), ε-caprolactone, paradioxanone (1,4-dioxan-2-one), trimethylenecarbonate (1,3-dioxan-2-one), alkyl derivatives of trimethylenecarbonate, monoglyceride polyesters, δ-valerolactone, β-butyrolactone,γ-butyrolactone, ε-decalactone, hydroxybutyrate, hydroxyvalerate,1,4-dioxepan-2-one (including its dimer1,5,8,12-tetraoxacyclotetradecane-7,14-dione), 1,5-dioxepan-2-one,6,6-dimethyl-1,4-dioxan-2-one 2,5-diketomorpholine, pivalolactone,alpha, alpha-diethylpropiolactone, ethylene carbonate, ethylene oxalate,3-methyl-1,4-dioxane-2,5-dione, 3,3-diethyl-1,4-dioxan-2,5-dione,6,8-dioxabicycloctane-7-one and polymer blends thereof.

The biocompatible, bioabsorbable inorganics include fine powders ofceramics composed of mono-, di-, tri-, alpha-tri, beta-tri, andtetra-calcium phosphate, hydroxyapatite, fluoroapatites, calciumsulfates, calcium fluorides, calcium oxides, calcium carbonates,magnesium calcium phosphates, bioglasses, and mixtures thereof.

Particularly preferred coating materials are bioabsorbable aliphaticpolyester waxes made by the polycondensation of monoalkanoyl glyceridesand common dicarboxylic acids (MGPEs=monoglyceride polyesters). TheseMGPE's have an aliphatic polyester backbone with pendant fatty acidester groups and exhibit relatively low melting points (T_(m)<100° C.).

A second preferred coating material is a copolymer ofepsilon-caprolactone and glycolide and glycolic acid. This compositionis more fully discussed in U.S. Pat. No. 4,994,074, issued Feb. 19,1991, the disclosure of which is hereby incorporated herein byreference. It is biocompatible and bioabsorbable, and approved by theFDA as a suture coating. Another preferred copolymer from this family ofcopolymers is a copolymer of 90% epsilon-caprolactone and 10% glycolicacid.

The inorganic fine powders mentioned above can also be added to thecoating polymer or attached to the top surface of the coating polymer toreduce the friction further by reducing the contact surface area and/orthrough ball bearing mechanism. There are other side benefits for addingceramic particles as they promote/induce bone growth and reduce tissueresponse by neutralizing the local acidic environment resulted bydegradation of the absorbable polymer.

Various bioactive agents such as proteins (including short chainpeptides), growth agents, chemotatic agents and therapeutic agents canbe added to the coating prior to applying the coating to the implantablemedical device. The variety of different therapeutic agents that can beused in conjunction with the present invention is vast. In general,therapeutic agents which may be administered include, withoutlimitation: anti-infectives such as antibiotics and antiviral agents;chemotherapeutic agents (i.e. anticancer agents); anti-rejection agents;analgesics and analgesic combinations; anti-inflammatory agents;hormones such as steroids; growth factors (bone morphogenic proteins(i.e. BMPs 1-7), bone morphogenic-like proteins (i.e. GFD-5, GFD-7 andGFD-8), epidermal growth factor (EGF), fibroblast growth factor (i.e.FGF 1-9), platelet derived growth factor (PDGF), insulin like growthfactor (IGF-I and IGF-II), transforming growth factors (i.e. TGF-βI-III), vascular endothelial growth factor (VEGF)); and other naturallyderived or genetically engineered proteins, polysaccharides,glycoproteins, or lipoproteins.

Coatings containing bioactive materials may be formulated by mixing oneor more therapeutic agents with the coating. The therapeutic agents maybe liquid, finely divided solid, or any other appropriate physical form.Optionally, the coating may include one or more additives, such asdiluents, carriers, excipients, stabilizers or the like. The type ofcoating and bioactive concentration can be varied to control the releaseprofile and the amount of bioactive dispensed. Upon contact with bodyfluids, the bioactive will be released. If the bioactive is incorporatedinto the coating, then the bioactive is released as the coatingundergoes gradual degradation. This can result in prolonged delivery(for example, typically over 1 to 5,000 hours, preferably 2 to 800hours) of sufficiently effective amounts of the bioactive.

Conventional coating techniques such as solution coating, powder coatingand melt coating can be applied to coat the devices. An example for thecopolymer of epsilon-caprolactone and glycolide and glycolic acid issolution coating. The coating polymer can be dissolved in an organicsolvent such as ethyl acetate. Solution coating techniques such as dipcoating, spraying, can then be used to coat the implantable medicaldevices.

For example, coating of the sheath expanding member 260 discussed abovecould be performed using a spray apparatus as described below. Theapparatus includes: a mounting fixture attached to a motor to gripmember 260 so that member 260 can be rotated around its longitudinalaxis during the coating process. A conventional coating spray gun ismounted on a conventional motorized x-table that can be translated alongthe length of member 260. A liquid coating is placed in the spray gun,and the settings of the spray gun, the distance from the spray gun tothe sheath expanding member 260, and the speeds of the rotating andtranslating motors can be adjusted so that the spraying is controllableand consistent to provide a uniform coating having a desired thickness.

The solvent used in dissolving the coating material often dissolves thebioabsorbable biopolymer used to make the device. In another embodiment,a substrate or base coat can be first coated on the surface of device toprotect the direct contact of the solvent. The base coat should also bebioabsorbable and may be applied in the form of an aqueous solution. Theaqueous base coat layer can be polyethylene glycol, modified starch,sucrose, dextrin, gelatin, acacia gum, poly (vinyl alcohol),hydroxypropyl methylcellulose, hydroxypropyl cellulose and carboxymethylcellulose.

The following examples are illustrative of the principles and practiceof the present invention, although not limited thereto. Numerousadditional embodiments within the scope and spirit of the presentinvention will be apparent to those skilled in the art.

EXAMPLE 1

This example describes the process for making an exemplary bioabsorbableimplantable medical device which may be used in accordance with anexemplary embodiment of the present invention.

Bioabsorbable graft ligament anchor systems 200 of the presentinvention, including a sheath member 220 and sheath expansion member 260were manufactured using a conventional injection molding process. Thepolymer used to manufacture the radially expandable sheath members 220was poly(lactic acid), or PLA, produced by Purac (Gorinchem, TheNetherlands), with an I.V. of 1.87 dL/g as measured in chloroform. Theexpandable sheath members 220 were injection molded on a Niigata NN35MIinjection molder with a barrel diameter of 18 mm. The polymer used tomanufacture the sheath expanding elements was poly(lactic acid), or PLA,produced by Purac (Gorinchem, The Netherlands), with an I.V. of 3.2-4.0dL/g as measured in chloroform. The sheath expanding members 220 wereinjection molded on a commercially available Engel injection molder witha 0.8 ounce barrel manufactured by Engel North America, Chicago, Ill.

A coating for the sheath expanding members 260 of the graft ligamentanchor system 200 was then prepared. The coating was a copolymer of 90%epsilon-caprolactone and 10% glycolic acid (Ethicon Incorporated,Somerville, N.J.) with an I.V. of 0.45 dL/g as measured inhexafluoroisopropanol (HFIP) at 25° C. dissolved in ethyl acetate to asolution concentration of 7.5%. The coating was applied using a sprayapparatus as described above. The x-table moving speed was set at 0.45mm/sec. The rotating speed was set at 46 RPM. The distance of the spraynozzle was 1 inch from the outer threads of the expansion member 260.The spray gun (Model 150, Badger Air-Brush Co., Franklin Park, Ill.)opening setting was two rotations away from the minimum opening. A firstsheath expanding member 260 was sprayed from the distal end to theproximal end and back, resulting in two passes of the sheath expandingmember 260 through the spray nozzle. A second sheath expanding member260 was sprayed as above, except the two-pass method was repeated threemore times, resulting in eight passes of the member 260 through thespray nozzle. The coated devices were then put under vacuum at roomtemperature for one hour to remove the solvent. The amounts of coatingwere calculated by measuring the weights of the respective members 260prior to and after the coating/drying steps. The sheath expanding member260 which passed through the spray nozzle two times was coated with 1.0milligram of coating, while the member 260 which passed through thespray nozzle eight times was coated with 4.5 milligrams of coating.These weights of coating represented between 0.065 and 0.290 weightpercent of the coating/sheath expanding member 260 combination,respectively, for the two coated members 260 elements.

The torque of inserting the coated and uncoated sheath expanding members260 into radially expandable sheaths 220 was then measured. Pilot holes,11.5 mm in diameter, were drilled in a model bone material (15 PCDFSawbone®, Pacific Research Laboratories, Inc., Vashon Island, Wash.).Four segments of Gore-Tex® Joint Sealant (W.L. Gore & Associates, Inc.,Elkton, Md.) were placed in each quadrant of the pilot hole to simulatethe hamstring tendons. A radially expandable sheath member 220 wasinserted inside the pilot hole so that the joint sealant segments werebetween the sheath member 220 and the walls of the pilot hole. Thedistal end of a sheath expanding member 260 was inserted into thecentral lumen 240 of the expandable sheath member 220. A digital torquegauge (Digital Torque Gauge Model TMG, IMADA Incorporated, Northbrook,Ill.) was used to measure the insertion torque. The IMADA digital torquegauge comprised of a driver and a torque meter. The driver was connectedto the torque meter so that the torque was measured and recorded in thetorque meter. The driver was disposed into the central cannulation ofthe sheath expanding member 260. The insertion torque was measured usingthe torque meter. The peak insertion torque values required to drive theexpanding member into the sheath central lumen 240 for an uncoated, anda two- and eight-pass coated expanding member 260 were 20, 6.9, and 7.9in-lb, respectively. The test results showed improved lubricity, andreduced tissue drag for coated devices.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes inform and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

What is claimed is:
 1. A medical method, comprising: implanting in apatient a first bioabsorbable implantable article having at least onefastener receiving opening, the fastener receiving opening having acontact surface with a first bioabsorbable lubricating coating disposedthereon; and disposing a bioabsorbable fastener within the at least onefastener receiving opening of the implanted first bioabsorbableimplantable article in mating engagement therewith such that a secondbioabsorbable lubricating coating formed on an outer surface of thebioabsorbable fastener contacts and moves relative to the firstbiocompatible lubricating coating on the contact surface of the firstbioabsorbable implantable article.
 2. The method of claim 1, wherein thecontact surface includes a sidewall of the at least one fastenerreceiving opening.
 3. The method of claim 1, wherein the firstbioabsorbable implantable article includes a plate member, the platemember including a top surface and a bottom surface, wherein the atleast one fastener receiving opening extends between the top surface andthe bottom surface, and implanting the first bioabsorbable implantablearticle comprises engaging the bottom surface with a tissue of thepatient.
 4. The method of claim 1, wherein implanting the firstbioabsorbable implantable article comprises engaging the firstbioabsorbable implantable article with hard tissue, and disposing thebioabsorbable fastener within the at least one fastener receivingopening comprises advancing the bioabsorbable fastener into the hardtissue to maintain the hard tissue in a desired position.
 5. The methodof claim 4, wherein the hard tissue comprises bone.
 6. The method ofclaim 1, wherein the first bioabsorbable implantable article includes anexpandable sheath member, the expandable sheath member including aproximal end, a distal end, and a central lumen defined by a wallextending between the proximal and distal ends.
 7. The method of claim6, wherein the expandable sheath member includes a proximal opening atthe proximal end that is in communication with the central lumen.
 8. Themethod of claim 6, wherein the contact surface includes an inner wallthat defines the central lumen.
 9. The method of claim 6, whereindisposing the bioabsorbable fastener within the at least one fastenerreceiving opening expands the sheath member.
 10. The method of claim 1,wherein implanting the first bioabsorbable implantable article comprisesengaging the first bioabsorbable implantable article with soft tissue,and disposing the bioabsorbable fastener within the at least onefastener receiving opening comprises advancing the bioabsorbablefastener into the soft tissue to maintain the soft tissue in a desiredposition.
 11. The method of claim 10, wherein the soft tissue comprisesone of tendon and ligament tissue.
 12. The method of claim 1, whereinthe first coating is different than the second coating.
 13. The methodof claim 1, wherein at least one of the first and second bioabsorbablelubricating coatings is a continuous coating.
 14. The method of claim 1,wherein at least one of the first bioabsorbable implantable article andthe bioabsorbable fastener are formed from a polymer selected from thegroup consisting of polylactic acid, polyglycolic acid,polycaprolactone, polydioxanone, trimethylene carbonate, and copolymersand blends thereof.
 15. The method of claim 1, wherein at least one ofthe first and second bioabsorbable lubricating coatings comprises apolymer selected from the group consisting of polylactic acid,polyglycolic acid, polycaprolactone, monoglyderide polyesters, andcopolymers and blends thereof.
 16. The method of claim 1, wherein atleast one of the first and second bioabsorbable lubricating coatingscomprises 90/10 polycaprolactone/polyglycolide copolymer.
 17. The methodof claim 1, wherein at least one of the first and second bioabsorbablelubricating coatings has a thickness in the range of about 1 microns toabout 10 microns.
 18. A medical method, comprising: implanting in apatient a bioabsorbable medical device including a first bioabsorbablecontact surface and a second bioabsorbable contact surface such that thesecond bioabsorbable contact surface engages the first bioabsorbablecontact surface, a bioabsorbable lubricating coating being disposed onat least a section of each of the first and second contact surfaces suchthat the first and second contact surfaces are moveable with respect toeach other, thereby reducing device drag between the first and secondcontact surfaces.
 19. A medical method, comprising: implanting in apatient a bioabsorbable medical device including a first member having afirst contact surface and a second member having a second contactsurface such that the second member engages the first member, abioabsorbable lubricating coating being disposed on at least a portionof the first and second contact surfaces such that the first and secondcontact surfaces engage each other and are moveable with respect to eachother, thereby providing reduced device drag between the first andsecond contact surfaces.